The blocking index of Tibaldi and Molteni (1990) was modified from that of Lejenas and Okland (1983). The index is local and instantaneous, ideally suited for real-time atmospheric monitoring, isolating regions of easterly flow at 500 hPa associated with high-latitude blocks.

This dataset uses the blocking index calculation for the northern hemisphere, however the index can be easily modified to examine blocking in the southern hemisphere. Blocking in the southern hemisphere typically occurs at lower latitudes when compared with the northern hemisphere. The index follows Tibaldi et al. (1994).